1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a light weight and highly cooled turbine rotor blade.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a turbine section in which a very high temperature gas flow passes through multiple rows or stages of rotor blades to drive the rotor shaft and other parts of the engine or, in the case of an industrial gas turbine engine, an electric generator to produce electrical power. Engine designers are constantly seeking ways to improve the engine performance, such as increasing the turbine inlet temperature (TIT) or providing more advanced airfoil cooling and preferably with less cooling air flow. Improved materials can also be used to allow for greater temperature exposure of the engine parts exposed to higher temperatures such as the airfoils in the stator vanes and rotor blades.
Current prior art rotor blades and stator vanes are formed as a single piece with the internal cooling passages formed into the airfoil. The investment, casting process is used to produce, for example, a turbine rotor blade from a nickel based superalloy in which the internal serpentine flow cooling circuit is formed by a core that is leached out during the manufacturing process. Film cooling holes are then drilled into the airfoil surface to provide for the discharge of film cooling air to provide additional cooling protection to the airfoil. This type of blade can be very heavy and expensive to produce. The investment casting process for a turbine airfoil results in a large number of defective castings because of the very fine and small internal cooling passages required in the airfoil. These passages are formed by the ceramic cores, and these small and fine ceramic cores often break during handling or the casting process. When a blade is cast, the molten metal forms the passages around the ceramic core. If a piece in the core that represents a cooling passage is broken, then the passage that forms around the metal will be incomplete or not even connected.